(1) Field of the Invention
The present invention relates to novel bis(arylsulfonylaminocarbonylaminobenzoate) compounds and to thermosensitive recording materials containing the same for forming colored images upon heating. More particularly, the present invention relates to novel bis(arylsulfonylaminocarbonylaminobenzoate) compounds and thermosensitive recording materials containing the same and having a high whiteness, an excellent colored image-retaining stability, due to which the color-developed images are not erased, and a high recording sensitivity.
The thermosensitive recording materials of the present invention contains the above-mentioned specific compounds as color-developing components, exhibit a high recording sensitivity and a high whiteness, can record thereon colored images having a good storage property over a long time, and have a high environmental resistance such as a high humidity resistance, a high oil resistance and a high plasticizer-resistance. Thus the thermosensitive recording materials of the present invention are usable for image-recording sheets, cash-dispenser sheets, ticket cards, commuting ticket cards, labels, for example, POS labels, cards, for example, prepaid cards, and pass cards.
(2) Description of the Related Art
Generally, a thermosensitive recording material comprises a substrate comprising a paper sheet, a synthetic paper sheet or a plastic film and a thermosensitive colored image-forming layer formed on the substrate and comprising, as principal components, a color-forming component, for example, an electron-donative leuco dye and a color-developing component comprising an organic acid substance, for example, an electron-acceptive phenol compound. The above-mentioned two components react with each other upon heating to form colored images. This type of thermosensitive recording material is disclosed in Japanese Examined Patent Publication No. 43-4,160, No. 45-14,039 and No. 48-27,736, and is employed in practice.
The thermosensitive recording material is compact, cheap and is easy to maintain, and thus is used in a broad range of practical applications, for example, outputs of computers, facsimiles, automatic ticket vending machines, printers for scientific and measurement equipments, printer for CRT medical measurements and the like. However, in the conventional thermosensitive recording materials, in which a thermosensitive colored image-forming layer contains a color-forming dye component, a color-developing component and a binder, the color-forming reaction is reversible and thus it is known that the colored images is erased with the lapse of time. The color-erasure is accelerated when the images are exposed to light, a high humidity atmosphere or a high temperature atmosphere. The color-erasure is further promoted by immersing in water for long period or by contacting with an oil, for example, salad oil, or with a plasticizer, to such an extent that the images cannot be read or noted.
Regarding the thermosensitive colored image-forming layer using a color-forming system containing a dye precursor including, as a principal component, a colorless or light colored lactone cyclic compound, many attempts to control the color-erasing phenomenon have been made. For example, in one attempt, a phenol compound-containing antioxidant is contained in the thermosensitive colored image-forming layer, as disclosed in Japanese Unexamined Patent Publication No. 60-78,782, No. 59-167,292, No. 59-114,096 and No. 59-93,387; in another attempt, a protective layer is formed from a hydrophobic polymer emulsion on the thermosensitive colored image-forming layer, as disclosed in Japanese Unexamined Patent Publication No. 56-146,796; in still another attempt, the thermosensitive colored image-forming layer is coated with an intermediate layer formed from an emulsion of a water-soluble polymeric compound or a hydrophobic polymeric compound, and the intermediate layer is coated by a surface layer formed from a oily lacquer containing, as a resin component, a hydrophobic polymeric compound, as disclosed in Japanese Unexamined Patent Publication No. 58-199,189; in still another attempt, a phenol compound-containing color developing agent is employed in combination with an epoxy compound, as disclosed in Japanese Unexamined Patent Publication No. 62-164,579; and in further another attempt, a metal salt of a specific salicylic acid derivative is employed as a color-developing agent, as disclosed in Japanese Unexamined Patent Publication No. 62-169,681.
It has been found that the anti-oxidative phenol compound contained in the thermosensitive colored image-forming layer does not contribute to improving the oil resistance of the resultant colored images (a retention of the color density of the colored images a fixed time after a salad oil is brought into contact with the colored images) and the plasticizer resistance of the resultant colored images (a retention of the color density of the colored images a fixed time after a plasticizer is brought into contact with the colored images), in comparison with those on the comparative thermosensitive colored image-forming layer containing no anti-oxidative phenol compound.
Also, in the thermosensitive recording material having the protective layer or the surface layer as mentioned above, the erasure of the colored images due to contact with the oil or plasticizer for a short time can be restricted, but the erasure of the colored images due to the contact with the oil or plasticizer over a long period cannot be prevented, and thus the protective layer and the surface layer are not recognized as essential means for solving the above-mentioned problems.
Further, when the phenol compound is employed in combination with the epoxy compound, a time necessary to stabilize the colored images formed by applying a heating procedure imagewise to the resultant thermosensitive colored image-forming layer, is relatively long. Thus when a salad oil or a plasticizer is brought into contact with the colored images immediately after the colored images are formed on the colored image-forming layer, the colored images are erased to a certain extent.
When the metal salt of the specific salicylic acid derivative is used for the thermosensitive recording material, the retention of the colored images can be improved, but a heat resistance test applied to the thermosensitive recording material causes the non-recorded white portions of the recording material to be colored. Also, the specific salicylic acid derivative is disadvantageous in that the chemical structure of the derivative is complicated and thus the derivative is too expensive.
Generally, to enhance the storage stability of the thermosensitive recording material, a specific additive or a special color-forming material must be used, and thus the resultant colored image-forming layer generally exhibits a relatively low thermosensitivity.
Japanese Unexamined Patent Publication No. 62-19,485 discloses specific color-developing compounds having a sulfonylamide group. The resultant thermosensitive recording material exhibits, however, a color-forming performance the same as or lower than that of the conventional thermosensitive recording material containing the conventional color-developing phenol compound. Namely, the specific color-developing compounds failed to provide an excellent color-forming performance.
An object of the present invention is to provide a thermosensitive recording material having a high whiteness, a satisfactory resistance of non-recorded portions thereof to unwilling color-development in hot environment, an excellent storage stability including high resistances to oils and plasticizers over a long period, and a high thermosensitivity for color-formation, and new color-developing compounds useful for the thermosensitive recording material.
Another object of the present invention is to provide a thermosensitive recording material not only useful for thermosensitive recording traveller""s tickets for ticket-vending machines, coupon ticket cards and commuter""s ticket cards which must have a high storage stability, labels for barcode system for POS which labels are adhered to a surfaces of packages of foods packed with polyvinyl chloride films and are most likely brought into contact with oils or plasticizers, but also useful as recording sheets of facsimile machines and word processor machines which sheets must have a high sensitivity for recording and a high storage stability, and recording sheets for image printers for CRTs, and new bis(arylsulfonylaminocarbonylaminobenzoate) compounds to be contained as color-developing agents in the recording material.
The above-mentioned objects can be attained by the thermosensitive recording material of the present invention and the new bis(arylsulfonylaminocarbonylaminobenzoate) compounds of the present invention.
The thermosensitive recording material of the present invention comprises substrate sheet and a thermosensitive colored image-forming layer formed on at least one surface of the substrate sheet and comprising at least one colorless or light-colored dye precursor, a color-developing agent reactive with the dye precursor upon heating to thereby develop a color, and a binder,
wherein the color developing agent comprises at least one compound of the formula (I): 
wherein R1 represents a member selected from the group consisting of unsubstituted aryl groups and substituted aryl groups with at least one substituent selected from the group consisting of a methyl group and a chlorine atom, and R2 represents a divalent organic group having 3 or more carbon atoms.
In the thermosensitive recording material of the present invention, the divalent organic group represented by R2 in the formula (I) is preferably selected from the group consisting of:
xe2x80x94(CH2)mxe2x80x94 groups, and
xe2x80x94(CH2CH2O)nxe2x80x94CH2CH2xe2x80x94 groups
wherein m represents an integer of 3 to 30, and n represents an integer of 1 to 20.
In the thermosensitive recording material of the present invention, the color-developing compound of the formula (I) is preferably selected from the compounds of the formulae (II), (III) and (IV): 
In the thermosensitive recording material of the present invention, the color-developing agent optionally further comprises, in addition to the compound of the formula (I), at least one compound of the formula (V): 
wherein R3 represents a member selected from the group consisting of unsubstituted aryl groups and substituted aryl groups with at least one substituent selected from the group consisting of a methyl group and a chlorine atom, and R4 represents a member selected from the group consisting of alkyl groups having 3 or more carbon atoms, aralkyl groups and aryloxyalkyl groups.
In the thermosensitive recording material of the present invention, the compound of the formula (V) is preferably that of the formula (VI): 
The bis(arylsulfonylaminocarbonylaminobenzoate) compound of the present invention is of the formula (I): 
wherein R1 represents a member selected from the group consisting of unsubstituted aryl groups and substituted aryl groups with at least one substituent selected from the group consisting of a methyl group and a chlorine atom, and R2 represents a divalent organic group having 3 or more carbon atoms.
In the bis(arylsulfonylaminocarbonylaminobenzoate) compound of the formula (I) of the present invention, the divalent organic group represented by R2 is preferably selected from the group consisting of a xe2x80x94(CH2)mxe2x80x94 group and a xe2x80x94(CH2CH2O)nxe2x80x94CH2CH2xe2x80x94 group wherein m represents an integer of 3 to 30 and n represents an integer of 1 to 20.
The bis(arylsulfonylaminocarbonylaminobenzoate) compound of the present invention is preferably selected from the group consisting of:
1,3-trimethylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate) of the formula (II): 
1,8-(3,6-dioxaoctylene)bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate) of the formula (III): 
and 1.9-nonamethylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate) of the formula (IV): 
The compound of the formula (I) and the optional compound of the formula (V) used in the thermosensitive colored image-forming layer of the present invention serve as color-developing agents. Namely, although the compounds of the formula (I) and the formula (V) have no acid functional group, for example, phenolic hydroxyl group and carboxyl group, they exhibit a strong color-developing property to basic leuco dye. The strong color-developing property is assumed to be due to a phenomenon in which the urea groups in the compounds of the formulae (I) and (V) are activated by the sulphonyl group located adjacent to the urea group.
The compounds represented by the general formula (I) are novel compounds. In the formula (I), the group represented by R1 is selected from the group consisting of unsubstituted aryl groups and substituted aryl groups with at least one substituent selected from the group consisting of a methyl group and a chlorine atom. Particularly, R1 is preferably selected from a phenyl group, a 2-naphthyl group, a p-tolyl group, an o-tolyl group, a m-tolyl group and a p-chlorophenyl group.
In the formula (I), the group represented by R2 is not specifically limited to specific groups, as long as the R2 group is a divalent organic group having 3 or more carbon atoms. Preferably, the group represented by R2 is a member selected from the following group.
(a) Divalent aliphatic or cycloaliphatic hydrocarbon groups having chemical structures corresponding to those of aliphatic or cycloaliphatic hydrocarbons from each of which structures two hydrogen atoms are excluded, particularly xe2x80x94(CH2)mxe2x80x94 groups in which m represents an integer of 3 to 30.
Preferably, the group (a) includes trimethylene, tetramethylene, pentamethylene, hexamethylene and nonamethylene groups, and substituted or branched or cyclic divalent hydrocarbon groups, for example, 1-methyl-1,3-trimethylene, 2,3-dimethyl-1,4-tetramethylene, 1,4-cyclohexylene, 1,4-cyclohexane dimethylene groups.
(b) Divalent hetero-aliphatic or cycloaliphatic hydrocarbon groups having chemical structures corresponding to those of hetero-aliphatic and cycloaliphatic hydrocarbons from each of which structures two hydrogen atoms are excluded, particularly xe2x80x94(CH2CH2O)nxe2x80x94CH2CH2xe2x80x94 group wherein n represents an integer of 1 to 20.
Preferably, the group (b) includes 1,5-(3-oxapentylene), 1,5-(3-thiopentylene), 2,5-(1-oxacyclohexylene), 1-oxacyclohexane-2,5-dimethylene, 1,8-(3,6-dioxaoctylene) and 1,12-(3,6,9-trioxadodecylene) groups.
(c) Divalent alkyl- or heteroalkyl-substituted aryl groups having chemical structure corresponding to those of alkyl-substituted aryl compounds or heteroalkyl-substituted aryl compounds, in each of which structures, two hydrogen atoms are excluded, from the alkyl group or the hetero atom-substituted group.
Preferably, the group (c) include an xcex1,xcex1xe2x80x2-(p-xylylene) group, an xcex1,xcex1xe2x80x2-(m-xylylene) group, a xcex2,xcex2xe2x80x2-(1,4-di(dimethylene)benzene) group, a xcex3,xcex3xe2x80x2(1,4-di(trimethylene)benzene) group and a xcex2,xcex2xe2x80x2-hydrogen atoms-excluded p-hydroquinone-diethylether group.
Examples of the compound of the formula (I) usable as a color developing agent of the present invention are shown below.
1,3-trimethylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
1,3-trimethylene bis(4-(o-toluenesulfonylaminocarbonylamino)benzoate),
1,3-trimethylene bis(4-(m-toluenesulfonylaminocarbonylamino)benzoate),
1,4-tetramethylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
1,4-tetramethylene bis(4-(o-toluenesulfonylaminocarbonylamino)benzoate),
1,4-tetramethylene bis(4-(m-toluenesulfonylaminocarbonylamino)benzoate),
propylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
propylene bis(4-(o-toluenesulfonylaminocarbonylamino)benzoate),
propylene bis(4-(m-toluenesulfonylaminocarbonylamino)benzoate),
1,5-(3-oxapentylene) bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
1,5-(3-oxapentylene) bis(4-(m-toluenesulfonylaminocarbonylamino)benzoate,
1,8-(3,6-dioxaoctylene) bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
1,12-(3,6,9-trioxadodecylene) bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
1,9-nonamethylene bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate),
xcex1,xcex1xe2x80x2-(1,4-cyclohexanedimethylene) bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate,
xcex1,xcex1xe2x80x2-(1,4-cyclohexanedimethylene) bis(4-(o-toluenesulfonylaminocarbonylamino)benzoate),
xcex1,xcex1xe2x80x2-(p-xylylene) bis(4-(p-toluene sulfonylaminocarbonylamino)benzoate),
xcex1,xcex1xe2x80x2-(p-xylylene) bis(4-(m-toluenesulfonylaminocarbonylamino)benzoate).
These compounds of the formula (I) may be employed alone or in a combination of two or more thereof.
The bis(arylsulfonylaminocarbonylamino benzoate) compounds of the formula (I) are novel compounds. Also, 1,3-trimethylene bis(4-p-toluenesulfonylaminocarbonylamino)benzoate) of the formula (II), 1,8-(3,6-dioxaoctylene) bis(4-(p-toluenesulfonylaminocarbonylamino)benzoate) of the formula (III) and 1,9-nonamethylene bis(4-(p-toluene sulfonylaminocarbonylamino)benzoate) of the formula (IV) are novel compounds useful as color developing agents, of the thermosensitive recording material of the present invention.
In the color-developing agent for the thermosensitive colored image-forming layer of the present invention, at least one compound represented by the general formula (V) is optionally contained in addition to the compound of the formula (I). In the formula (V), R3 represents a member selected from the group consisting of unsubstituted aryl groups and substituted aryl groups with at least one substituent selected from the group consisting of a methyl group and a chlorine atom. Preferably, the R3 group is selected from phenyl, z-naphthyl, p-tolyl, o-tolyl, m-tolyl and p-chlorophenyl groups.
Also, in the formula (V), R4 represents a member selected from the group consisting of alkyl groups having 3 or more carbon atoms, aralkyl groups and aryloxyalkyl groups. The alkyl group for R4 is preferably selected from n-propyl, isopropyl, n-butyl, isobutyl, hexyl, cyclohexyl and octyl groups. The alkyl group for R4 preferably has 3 to 8 carbon atoms. When the alkyl group represented by R4 has 2 or less carbon atoms, the resultant color-developing compound exhibits a high melting temperature and thus the resultant thermosensitive recording material containing the compound having the high melting temperature may exhibit an unsatisfactory sensitivity. When the alkyl group for R4 has more than 8 carbon atoms, the resultant compound may exhibit an unsatisfactory dispersing property. The aralkyl group represented by R4 is preferably selected from benzyl, phenethyl, 2-naphthylmethyl, and 2-naphthylethyl groups. Further, R4 may represent an aryloxyalkyl group in which an alkyl moiety is connected to an aryl moiety through an oxygen atom, for example, a phenoxyethyl or 2-naphthoxyethyl group.
Preferably, the color developing compound of the formula (V) is selected from
propyl 4-(p-toluenesulfonylaminocarbonylamino)benzoate,
propyl 4-(m-toluenesulfonylaminocarbonylamino)benzoate,
propyl 4-(o-toluenesulfonylaminocarbonylamino)benzoate,
propyl 4-(benzenesulfonylaminocarbonylamino)benzoate,
propyl 4-(p-chlorobenzenesulfonylaminocarbonylamino)benzoate,
propyl 4-(m-chlorobenzenesulfonylaminocarbonylamino)benzoate,
butyl 4-(p-toluenesulfonylaminocarbonylamino)benzoate,
butyl 4-(o-toluenesulfonylaminocarbonylamino)benzoate,
butyl 4-(m-toluenesulfonylaminocarbonylamino)benzoate,
benzyl 4-(p-toluenesulfonylaminocarbonylamino)benzoate,
benzyl 4-(m-toluenesulfonylaminocarbonylamino)benzoate,
cyclohexyl 4-(p-toluenesulfonylaminocarbonylamino)benzoate,
butyl 4-(p-chlorobenzenesulfonylaminocarbonylamino)benzoate, and
butyl 4-(o-chlorobenzenesulfonylaminocarbonylamino)benzoate.
These compounds of the formula (V) may be employed alone or in a combination of two or more thereof.
In the thermosensitive colored image-forming layer of the present invention, the leuco dyes usable as dye-precursors may be selected from conventional leuco dyes, for example, triphenylmethane dyes, fluoran dyes, and diphenylmethane dyes. Preferably, the dye precursor comprises at least one member selected from
3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide,
crystal violet lactone,
3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran,
3-diethylamino-6-methyl-7-anilinofluoran,
3-diethylamino-6-methyl-7-(o- or p-dimethylanilino)fluoran,
3-(N-ethyl-N-p-toluidino)-6-(methyl-7-anilino)fluoran,
3-pyrrolidino-6-methyl-7-anilino-fluoran,
3-dibutylamino-6-methyl-7-anilino-fluoran,
3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluoran,
3-diethylamino-7-(o-chloroanilino)fluoran,
3-diethylamino-7-(o-chloroanilino)fluoran,
3-dibutylamino-7-(m-trifluoromethylanilino)fluoran,
3-diethylamino-6-methyl-7-chlorofluoran,
3-diethylamino-6-methylfluoran,
3-cyclohexylamino-6-chlorofluoran,
3-(N-ethyl-N-hexylamino)-6-methyl-7-(p-chloroanilino)fluoran.
In the thermosensitive recording material of the present invention, unless the target effect of the present invention is damaged, a conventional color-developing compound may be employed in addition to the compound of the formula (I).
The additional color-developing compound may be selected from conventional color-developing phenolic compounds, compounds having only one sulfonylurea group per molecule thereof, and organic acids. The conventional color developing compounds are preferably selected from, for example, 2,2-bis(4-hydroxyphenyl)propane, namely bisphenol A, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,4-bis(1-methyl-1-(4xe2x80x2-hydroxyphenyl)ethyl)benzene, 1,3-bis(1-methyl-1-(4xe2x80x2-hydroxyphenyl)ethyl)benzene, dihydroxydiphenylethers (disclosed in Japanese Unexamined Patent Publication No. 1-180,382), benzyl p-hydroxybenzoate (disclosed in Japanese Unexamined Patent Publication No. 52-140,483), bisphenol S, 4-hydroxy-4xe2x80x2-isopropyloxydiphenylsulfone (disclosed in Japanese Unexamined Patent Publication No. 60-13,852), 1,1-di(4-hydroxyphenyl)cyclohexane, 1,7-di(4-hydroxyphenylthio)-3,5-dioxaheptane (disclosed in Japanese Unexamined Patent Publication No. 59-52,694), 3,3-diallyl-4,4xe2x80x2-dihydroxydiphenylsulfone (disclosed in Japanese Unexamined Patent Publication No. 60-208,286) and 2,4-bis(phenylsulfonyl)phenol (Japanese Unexamined Patent Publication No. 8-269,000).
In the thermosensitive recording material of the present invention, unless the target effect of the present invention is damaged, conventional thermo-fusible compounds may be contained, as a sensitizing agent, in the thermosensitive colored image-forming layer.
The typical fusible compounds are phenyl 1-hydroxy-2-naphthoate (Japanese Unexamined Patent Publication No. 57-191,089), p-benzylbiphenyl (Japanese Unexamined Patent Publication No. 60-82,382), benzylnaphthylether (Japanese Unexamined Patent Publication No. 58-87,094), dibenzyl terephthalate (Japanese Unexamined Patent Publication No. 58-98,285), benzyl p-benzyloxybenzoate (Japanese Unexamined Patent Publication No. 57-201,691), diphenyl carbonate and ditolyl carbonate (Japanese Unexamined Patent Publication No. 58-136,489), m-terphenyl (Japanese Unexamined Patent Publication No. 57-89,994), 1,2-bis(m-tolyloxy)ethane (Japanese Unexamined Patent Publication No. 60-56,588), 1,5-bis(p-methoxyphenoxy)-3-oxapentane (Japanese Unexamined Patent Publication No. 62-181,183), diesters of oxalic acid (Japanese Unexamined Patent Publication No. 64-1,583), and 1,4-bis(p-tolyloxy)benzene (Japanese Unexamined Patent Publication No. 2-153,783).
The thermosensitive colored image-forming layer of the thermosensitive recording material of the present invention optionally further contains waxes and preferably contains organic and inorganic pigments. The colored image-forming layer contains a binder for binding the components as mentioned above to the substrate.
In the thermosensitive colored image-forming layer, preferably, the color-forming leuco dye (dye precursor) is contained in a content of 5 to 20% by weight based on the total dry weight of the colored image-forming layer, and the color-developing agent including the compound of the formula (I) and optionally the compound of the formula (V) is contained in a content of 5 to 50% by weight based on the total dry weight of the colored image-forming layer. When the content of the color developing agent is less than 5% by weight, the color developing performance of the resultant colored image-forming layer may be insufficient, and when the content of the color developing agent is more than 50%, the color developing performance of the resultant colored image-forming layer may be saturated and an economical disadvantage may occur. When the sensitizing agent is employed, and when the content of the sensitizing agent is less than 5%, a satisfactory sensitizing effect on the colored image-forming layer may not be expected. Also, when the content of the sensitizing agent is more than 50% by weight, the sensitizing effect may be saturated and no further enhancement in the sensitivity of the colored image-forming layer may be expected.
Where the thermosensitive colored image-forming layer contains a conventional phenolic compound- or organic acid-containing color developing compound, the content of the conventional color-developing compound is preferably 5 to 40% by weight based on the total dry weight of the colored image-forming layer. When the sensitizing agent is contained, the content of the sensitizing agent is preferably 10 to 40% by weight based on the total dry weight of the colored image-forming layer. When the wax and the white pigments are contained, the contents of the wax and the white pigment are respectively 2 to 20% by weight and 2 to 50% by weight based on the total dry weight of the colored image-forming layer. Also, the binder is contained in a content of 5 to 20% by weight based on the total dry weight of the colored image-forming layer.
The white pigments for the thermosensitive colored image-forming layer are preferably selected from fine particulate inorganic white pigments, for example, calcium carbonate, silica, zinc oxide, titanium dioxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcinated clay, talc, and surface-treated calcium carbonate and silica pigments; and fine particulate organic white pigments, for example, urea-formaldehyde resin, styrene-methacrylate copolymer, and polystyrene resin pigments.
The wax usable for the present invention may be selected from conventional waxes, for example, paraffin waxes, amide waxes, bisimide waxes and higher fatty acid metal salt waxes.
The binder usable for the present invention preferably comprises at least one member selected from water-soluble polymeric materials, for example, various polyvinyl alcohols different in molecular weight from each other, starch and derivatives thereof such as oxidized starch, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose, sodium salt of polyacrylic acid, polyvinyl pyrrolidone, acrylic acid amide-acrylate ester copolymers, acrylic acid amide-acrylate ester-methacrylic acid terpolymers, alkali salts of styrene-maleic anhydride copolymers, polyacrylamide, sodium alginate, gelatin and casein; and latices of polyvinyl acetate, polyurethanes, styrene-butadiene copolymers, poly acrylic acid, polyacrylate esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers, and styrene-butadiene-acrylic monomer copolymers.
The substrate sheet usable for the present invention may be selected from paper sheets (acid paper sheets and neutral paper sheets), coated paper sheets produced by coating paper sheets with a pigment and/or a latex, laminate paper sheets, synthetic paper sheets made from, for example, a polyolefin resin, and plastic films.
The thermosensitive recording material is produced by coating at least one surface of the substrate sheet with a coating liquid containing the above-mentioned dye precursor, color-developing agent, binder, and optionally the above-mentioned additives, and drying the coating liquid layer on the substrate sheet. The amount of the coating liquid applied to the substrate sheet is controlled so that the resultant colored image-forming layer preferably has a dry weight of 1 to 15 g/m2, more preferably 2 to 10 g/m2.
In the thermosensitive recording material of the present invention, the thermosensitive colored image-forming layer is optionally coated with an uppercoat layer, for example, a protective layer or a printing layer. Also, optionally, an undercoat layer comprising a pigment, preferably an oil-absorbing pigment, and a binder, is formed between the substrate sheet layer and the thermosensitive colored image-forming layer.